Equipment
Pond weed
Retort stand clamp
Light source
Sodium carbonate
Test tube
Water
Ruler
Safety points
- Put the clamp right way or it will fall out. On the inside.
- Don’t touch the bulb when it is hot or else burn yourself.
Method
1. Fill a test tube with tap water and add one spatular of sodium carbonate solution.
2. Select a pondweed shoot about 10 cm long
3. Set up apparatus as shown in the diagram
4. Place a bench lamp 5cm away from the beaker, switch on and start the timer.
5. Record the number of bubbles produced in one minutes. (Repeat three times)
6. Repeat step 1-5, moving the bench lamp to 5cm each time away from the test tube.
This is the method we used in school and is much simpler to understand than others
Predictions
I predict that the closer the lamp is to the Testube of water with the pondweed, the faster the pondweed will photosynthesise. It will photosynthesis quicker if the lamp is closer because of the heat which will help the pondweed to photosynthesis. There is scientific proof that pondweed will photosynthesis quicker when light is closer. The chlorophyll uses light energy to perform photosynthesis. It can only do it as fast as the light energy is arriving. However, normally as the light intensity increases, so does the rate of reaction, but only up to a certain point, when another factor becomes limiting. As light intensity halves the rate of photosynthesis will halve. At anytime one or the other three factors will be the limiting factor which is keeping the photosynthesis down at the rate it is. As the light level is raised, the rate of photosynthesis increases steadily but only up to a certain point, beyond that, it won’t make any difference because then it’ll be either the temperature or the CO² level which is the limiting factor. As with light intensity the amount of CO² will only increase the rate photosynthesis up to a point. As long as light and CO² are in plentiful; supply then the factor limiting photosynthesis must be temperature
Result
These results were in the winter that’s why the rate of photosynthesis is low. There are three pairs of results because then the results will be more accurate. Another table has been because they results from the summer. If you do it three times the results will be similar and more accurate then you differently know the results are accurately. It is also useful to do it three times to find out if you have onolomous results
Conclusion
Using my results, I found my prediction is correct. The higher the light intensity, the more bubbles were produced. This proves my prediction is correct. My prediction is corrects as shown in the graph as I had said that if the light intensity increased the photosynthesis quicker, because after a certain point the line stays on the same level. The bubbles produced are bubbles of oxygen. In the chemical equation (Light + water → glucose + oxygen) for photosynthesis it states glucose and oxygen is produced from carbon dioxide and water. Perhaps there was a limiting factor in the process of photosynthesis there is a limiting factor but it only goes up to a certain point. It could be because the light was too far away or the change of surroundings. The temperature of water may not be accurate enough for photosynthesis for photosynthesis to take place, there may not be enough carbon dioxide or even too much. Whatever the reason the main conclusion for normal results is dependent on the light intensity. The method that was used was not that accurate because it only tells you the main steps of photosynthesis when it should tell you everything. Photosynthesis is light dependent. At low light intensities, this may become the limiting factor - one reason why plants grow better outdoors, rather than in the house, and one reason why we recommend the use of light banks if you are trying to grow plants in schools.
Evaluation
Overall, I would state the experiment as a success since my predictions were supported by my results. This is important in reflecting success only if my prediction was sensible and logical. Just as important is where the experiment was not a success and why. This photosynthesis investigation was probably not performed as accurately as it could have been due to some controllable and uncontrollable conditions it was not accurate because results did not come from a data logger we had to count bubbles if I was to do it again I would use the data logger. Some mistakes can be corrected. While performing the experiment, the piece of pondweed did not photosynthesize at a steady rate, even when the distance from the plant to the light source was kept a constant in the first results table. I had got anomalous because of the light intensity when the light was close the results were fine but when the light moves further back you start to get anomalous results because the light is further away this had effected my conclusion to overcome this problem you could only use one light source and probably change the water every time you move the light back. You could also add temperature into your test and add into your results. When you move the light back the bubbles decrease and that’s when the bubbles become to a Holt and that’s when it becomes a limiting factor.
Bibliography
Got some of the introduction from science help and from science book life processes.
Appendix
Results
Table
Graph 1
Table 2
Graph
Table 3
Graph
Graph 4
